Access to a patient's vascular system can be established by a variety of temporary and permanently implanted devices. Most simply, temporary access can be provided by the direct percutaneous introduction of a needle through the patient's skin and into a blood vessel. While such a direct approach is relatively simple and suitable for applications such as intravenous feeding, intravenous drug delivery, and other applications which are limited in time, they are not suitable for hemodialysis and other extracorporeal procedures that must be repeated periodically, often for the lifetime of the patient.
For hemodialysis and other extracorporeal treatment regimens, a variety of transcutaneous catheters and implantable ports have been proposed over the years. Prior medical transcutaneous catheters comprise a single catheter tube having a distal end placed in a vein in an in-dwelling manner and a proximal end which extends through the skin and which is available for connection to a hemodialysis or other blood treatment system.
Implantable infusion devices or ports, in contrast, are entirely subcutaneous and connected to a vein or an artery by a subcutaneous cannula. Access to the port is achieved by percutaneous placement of a needle or other connecting tube. Such ports typically comprise a needle-penetrable septum to permit percutaneous penetration of the needle. However, conventional ports do not allow the needle to penetrate deeply into the port. Because of this, a small displacement of the needle can cause it to be pulled from the port. In cases where locally toxic materials are being infused, extravasation of such materials can cause local tissue damage which may require corrective surgery such as skin grafting or removal of tissue. Recently, several valved-port designs have been proposed, where introduction of a needle or other access tube opens a valve to provide flow to the cannula which connects to the blood vessel.
Both the transcutaneous and subcutaneous implanted port vascular access systems described above suffer from certain disadvantages and limitations. For example, both such systems permit only limited blood flow rates. In the case of transcutaneous catheters, the limited flow rates result from the generally small lumen diameters available in in-dwelling catheters. In the case of implanted port access systems, the limited flow rates have resulted from both the port structure and the relatively small lumen diameters available in the cannulas which connect the port to the blood vessel. Such limited blood flow rates are problematic since they prolong the duration of the associated extracorporeal blood treatment protocol, such as hemodialysis, hemofiltration, and apheresis.
The subcutaneous placement of the catheter or cannula which is connected to or implanted within the blood vessel and brought to the external attachment point, i.e., either the implanted port or transcutaneous tract through the skin, is difficult in a number of respects. For, example, catheters and cannulas having their distal ends implanted in the jugular vein are typically bent by an angle from 90° to 180° to locate their associated ports or catheter exit points at an appropriate location on the patient's chest. Such bends also can accommodate excess length in connecting catheters and cannulas. The bends, however, are also subject to kinking and other problems.
One attempt at solving other problems is found in U.S. Pat. No. 5,387,192 to Glantz, et al. This patent disclosed a subcutaneously implantable access port, includes a two piece plastic jacket, comprised of a cowl and a base, which surrounds a metallic reservoir. The metallic reservoir has an open top and a closed bottom. The open top of the reservoir is sealed by the septum to define a chamber. The non-metallic cowl includes a septum opening and a flange positioned adjacent to the top of the opening. The non-metallic base includes a reservoir opening in which the metallic reservoir is received. The cowl and base are positioned to define a forming zone and are connected at the forming zone to substantially surround the metal reservoir.
One problem encountered such devices having fluid cavities and separate exit passageways through which the fluids will travel, is the formation in such devices of seams, having corners and edges. As blood or other fluids are injected into a fluid cavity, pressure develops within the cavity causing the fluid to flow through the exit passageway. As a result of the fluid flowing past these seams, edges and corners, turbulence may develop, which will affect some fluids, such as blood, which are sensitive to turbulence. A further problem with the reservoir cup is that dead spots are created in the areas where the floor of the cup meets the exit passageway retarding the fluid flow, leading to stagnation or the formation of clots or blockages in the port.
A series of U.S. Patents to William Ensminger, et al., discloses access ports having internal lumens for receiving a percutaneously introduced access device (e.g. a needle or catheter/stylet combination) and internal valve structures for isolating the port from an associated implanted catheter. These patents, disclose a number of specific valve types which may be incorporated within the access port, including leaflet valves, ball valves, flapper valves, and other specific configurations which are referred to as “articulating valves.” All such structures, however, generally require that the access device be passed through the valve itself (i.e., the portion which closes the blood flow path through the valve) in order to cause the valve to open. Such a requirement presents the risk that the valve will be degraded by direct contact with the access device after repeated uses so that portions of the valve may be degraded and released into circulation. Such valves also present a significant risk of failure after repeated use or contact with a sharpened needle. Additionally, such valve structures can damage the access device as it is being introduced therethrough, thus potentially disrupting valve flow through the needle during a subsequent treatment protocol.
In U.S. Pat. No. 5,704,915 to Melsky, et al., a dual access port for hemodialysis is comprised of a pair of conical or funnel-like shells joined tangentially at their outer surfaces, each shell having a relatively large entrance and a relatively small exit end. A self-sealing septum closes the entrance of each shell and a pair of outlet tubes extend from the exit ends of each shell. The conical configuration places the septum of each shell opposite the outlet tube so that when a needle accesses the port, it will lie in line with the outlet tube. A bend in the shell prevents the access needles from being advanced to a point where the needles can puncture the walls of the attached catheter. The shells include a carbon insert or liner to create a thromboresistant as well as scratch resistant surface over most of the shell's interior. In the areas which are likely to be contacted by the tip of the needle, pyrolitic carbon coating may be used. The remaining interior surface, for example at the outlet tube, can be titanium.
A problem with the Ensminger and Melsky devices is that the entry ports are usually inclined at a substantial angle relative to the skin surface through which the access device is introduced. Such angled access requires that the personnel introducing the access device guess the angle and estimate the optimum insertion point on the patient's skin. Such uncertainty in the device penetration is perhaps why these designs all require the use of enlarged “funnel” for receiving and aligning the needle as it is introduced. It would thus be advantageous to provide access ports having entry passages which are disposed generally “vertically” (i.e., at an angle which is substantially normal to the skin surface through which the needle is being introduced). By penetrating the needle “straight in,” it is much easier to align the needle with the target orifice and the size of the orifice area can be reduced.
Accordingly, there has been a need for an improved an implantable, subcutaneous single or multi-port vascular access device for hemodialysis and other drug delivery applications, which overcomes the above-noted problems.